The invention pertains to a shielding sheath for use with electronic cables. More particularly, it pertains to a tubular shielding sheath which may be formed from a flat strip, and is suited for use over a ribbon cable.
Shielding sheaths are commonly used to protect cables from external electromagnetic emissions and/or contain electromagnetic emissions from the cables. A typical sheath comprises a woven metallized fabric conductive shield surrounded by a flexible electrically insulating sheet.
In a prior sheath, the sheet is formed of polyurethane and has an inner surface covered by a layer of pressure-sensitive adhesive. The conductive shield is substantially in contact with and attached to the inner surface of the sheet via the adhesive. The shield is substantially the same width as the sheet, but is slightly laterally offset laterally of the sheath so as to create an overlap section of the shield extending beyond an edge of the sheet and an overlap section of the sheet extending beyond an opposite edge of the shield. A strip of release paper is disposed on the adhesive along the overlap section of the sheet.
To form the insulating sheet and attached shield into a tubular sheath, the release paper is first removed, exposing the adhesive layer. The overlap section of the insulating sheet is then wrapped over the opposite edge of the sheet and secured to the outer surface of the sheet along the opposite edge via the adhesive. Accordingly, the overlap section of the conductive shield is covered by the opposite edge of the shield such that the outer surface of the overlap section is in contact with the inner surface of the shield adjacent the opposite edge. The overlap assures electrical contact and that there is no gap for leakage of radiation. The tubular sheath is flattened by means of a heated roller to crease the edges for receiving a ribbon cable.
When a shielding jacket is made with conductive fabric on the inside and plastic sheet on the outside, there are some remaining problem areas. One significant one is the flammability of the shielding jacket due to the exposed fabric. Attempts have been made to alleviate this by coating the fabric, but they have not been adequate. Attempts have also been made to apply an adhesive tape inside the fabric layer, but these products have not been found to be manufacturable.
There is also appreciable friction between exposed fabric and the cable, which may make it difficult to insert cable in long lengths of shielding sheath.
One prior construction has a strip of metallized fabric extending inside the sheath for overlap to prevent radiation leakage. It is possible when inserting a ribbon cable into the sheath to place it on the wrong side of the strip of fabric, leaving a narrow gap in the shielding for radiation leakage.
A product has been designed with overlapping portions of a conductive fabric arranged in a flattened tubular sheath or jacket such that one edge portion is on one face of a ribbon cable, and the other edge portion of the fabric is on the opposite face of the ribbon cable. When one tries to fabricate such a construction with an insulating sheet on the inside, it is found to be extremely difficult to make.
It would be desirable to alleviate such shortcomings and make a flattened insulating sheath for a ribbon cable with encased electrical shielding which prevents leakage of radiation.